Cervical brachytherapy utilizing ring applicator: comparison of standard and conformal loading.

PURPOSE Afterloading high-dose-rate brachytherapy (HDR) treatment of cervical cancer with cross-sectional imaging and three-dimensional (3D) reconstruction offers opportunities for individualized conformal treatment planning rather than fixed point-A dosimetry. METHODS AND MATERIALS Between June 2003 and September 2004, 15 patients with FIGO Stage 1B-4A cervical carcinoma, median age 56 years, were treated with radical external-beam radiotherapy to pelvis, including paraortic nodes if positive on staging investigations. Fourteen patients received concurrent cisplatin chemotherapy. All patients received HDR brachytherapy administered by intrauterine tube and ring applicator. Clinical target volume (CTV) and organs at risk (OAR)--rectum, bladder, and small bowel--were outlined from postinsertion CT planning scans. Planning target volume (PTV) was derived by use of 2-mm to 3-mm 3D expansion. A standard plan was produced that delivered 6 Gy to point A, and a second plan delivered 6 Gy to PTV. Constraints were defined for the OAR: bladder, 6 Gy; rectum, 5 Gy; and small bowel, 5 Gy. Dosimetric comparison was performed by use of the Baltas conformal index (COIN). RESULTS Mean COIN values were 0.39 for conformal plans and 0.33 for standard plans (p = 0.001); mean D95 values were 4.79 Gy and 4.50 Gy, respectively. CONCLUSION The majority of patients achieved a plan closer to ideal for coverage of PTV, with minimization of radiation received by normal tissues for conformal loading measured by COIN compared with fixed point-A prescription that used the cervical ring applicator.